FISHERY BULLETIN: VOL. 80, NO. 3 



vived to first crab stage. The time period of 37 d 

 may well be a reasonable reflection of what takes 

 place in the plankton, because at 25°C in the lab- 

 oratory a hypothetical zoea passing through the 

 minimum duration for each stage could conceiv- 

 ably attain first crab stage in as few as 32 d (5 

 stages) or 38 d (6 stages) after hatching. 



The variation in duration of each zoeal stage at 

 25°C (except for the first zoea) was rather low, 

 comprising no more than 2 d. Stage I, however, 

 could last from 5 to lid, although most individ- 

 uals molted to stage II between 6 and 7 d after 

 hatching. A single zoea that remained in stage I 

 for lid also molted to stage II, but died the fol- 

 lowing day. A comparison of the values in Table 1 

 with the survival graph (Fig. 1) shows that mor- 

 tality was quite high on the days just prior to, and 

 during, the ecdysial period in stage I, but as 

 development progressed the mortality subse- 

 quently fell. These results are similar to others 

 obtained in our laboratory with brachyuran and 

 anomuran larvae, and indicate that the more 

 mature zoeal stages have a greater survival 

 potential. This might be a result of one or a com- 

 bination of factors, including the type, quality, 

 and amount of food consumed, the genetic make- 

 up of the parents, or a response by the larvae to 

 unfavorable physical conditions in the labora- 

 tory (see Bookhout and Costlow 1970; Knowlton 

 1974; Gore et al. 1981, for summaries of the vari- 

 ous hypotheses). 



At 20°C, both within-stage and overall devel- 

 opmental duration were more variable. Ex- 

 tended zoeal durations and the production of a 

 sixth zoeal stage were both noted at the cooler 

 temperature. Larvae remained in stage I 9-14 d 

 before proceeding with further development. 

 Most larvae molting to stage II did so 10 d after 

 hatching. However, a larger component of zoeae 

 died than survived during this ecdysis, most 

 dying at day 14, with 3 zoeae lasting until day 21. 

 It would seem that whatever general effect the 

 lower temperature has on zoeal stages cannot be 

 overridden after about 12-13 d in the first stage, 

 so that the larvae eventually die if they have not 

 molted by this time. Once stage II was reached, 

 most zoeae were capable of continuing their de- 

 velopment with relatively little mortality com- 

 pared to that seen in stage I (Fig. 1). Modal 

 values of within-stage developmental time were 

 generally twice that seen at 25°C. The rearing 

 data also show that the megalopal stage was at- 

 tained following 6, rather than 5, zoeal stages, 

 approximately 53-55 d after eclosion. Another 



18-25 d were required before the first crab stage 

 was reached. Thus, a minimum of 73 d was re- 

 quired after hatching to complete development, 

 even though an extrapolation from the minima 

 in Table 1 suggests that a hypothetical zoea 

 might possibly reach first crab stage in as few as 

 64 d after hatching at 20°C. Extended develop- 

 mental times such as these are not necessarily 

 detrimental if the larvae can avoid predation and 

 find sufficient and suitable food. Such longer 

 periods of development could aid in the dispersal 

 of the larvae, thereby accounting, at least in part, 

 for the wide distribution of the adults of this spe- 

 cies. However, at the lower temperature of 15°C, 

 all of the 48 larvae remained in stage I up to 12 d 

 before dying. This high mortality suggests very 

 unfavorable conditions for the survival of this 

 species. 



Cyclograpsus integer, along with some species 

 of Sesarma, is among the few Sesarminae, and 

 among still fewer Varuninae and Plagusiinae 

 (Wilson 1980; Wilson and Gore 1980) known to 

 have extra larval stages. The species presently 

 stands alone in the genus in having this feature, 

 but joins an increasingly large group of brachy- 

 uran (and anomuran) crustaceans in which an 

 additional larval stage occurs either at lower, or 

 perhaps suboptimum, temperatures (Sandifer 

 1973; Knowlton 1974; Scotto 1979; Gore et al. 

 1981). The studies just cited follow classic inves- 

 tigations by Costlow et al. (1960), Bookhout 

 (1972), and Bookhout and Costlow (1974) in 

 which temperature and salinity were manipu- 

 lated and the effects on survival, duration, and 

 number of larval stages were observed. The data 

 in all these studies add to a large body of circum- 

 stantial evidence from the plankton (e.g., alleged 

 substages, morphological variants, oversized 

 larvae, etc.) which suggests that additional lar- 

 val stages may be an integral part of a decapod 

 crustacean's larval potentiality in nature, and 

 not just an artifact observed during laboratory 

 culture of the species. Whether extra stages 

 occur commonly, or only rarely, they are still 

 classifiable as a response to change in conditions, 

 and as such constitute an evolutionary adapta- 

 tion toward survival. 



Description of the Larvae 



First Zoea 



Carapace length: 0.38 mm; 5 specimens exam- 

 ined. 



504 



